Spin-mediated electrocatalytic nitrate reduction to ammonia on two-dimensional transition metal borides

Electrochemical nitrate reduction reaction (NO₃RR) is attractive for its ability to effectively remove NO₃⁻ from sewage under ambient conditions and offer a promising green synthetic route for sustainable ammonia production. This process involves the transfer of eight electrons and nine protons and generation of various intermediates with abundant spin characteristics, thereby introducing an intricacy to the development of promising catalyst materials. Herein, a group of two-dimensional metal boride materials is utilized to elucidate the spin-mediated structure–activity relationship for NO₃RR catalysts by theoretical calculations and experimental validations. It is found that the moderate spin polarization strength of catalyst contributes to balancing the interaction between the key adsorbed species and catalyst, and the spin can be regarded as an effective descriptor to evaluate the activity of NO₃RR catalysts. As a proof-of-concept model, FeB is confirmed to exhibit moderate spin polarization and promising catalytic performance, achieving NH₃ yield of 10649.66 μg h⁻¹ cm⁻² at −0.7 V vs. RHE and a faradaic efficiency up to 74.59 %, as well as NO₃⁻ removal rate of 98.9 % under low concentration environmental wastewater conditions. This study provides valuable insights into the design of functional catalytic materials and the understanding of spin-mediated mechanism for electrochemical NO₃RR as well as other catalytic reactions in wastewater treatment.